With rising concern over the use of phosphate builders in detergent mixtures and their effects upon the environment, the use of alternative water softening agents in detergents has increased. One common alternative is zeolite (Na.sub.2 O.Al.sub.2 O.sub.3.nSiO.sub.2.xH.sub.2 O), the synthetic forms of which are sometimes referred to as molecular sieves. Zeolite A is the most common commercially employed zeolite in detergent mixtures. Zeolite A is normally used in combination with another softening agent, such as the tri-sodium salt of nitrilotriacetic acid (NTA). Such a separate softening agent is needed to remove large hardness ions (i.e. hydrated magnesium and iron). Zeolite A is ineffective for this purpose due to its small pore size. In contrast, Maximum Aluminum X-type zeolite (having a Si:Al ratio of below 1.2) has a larger pore size (than zeolite A) and removes both large and small hardness ions from aqueous solution; therefore a secondary softening agent, such as NTA, may be unnecessary with Maximum Aluminum X-type zeolite, or may be required in lesser amounts.
The known prior art methods for preparation of "Reduced Silica" or "Low Silica" X-type zeolites (sometimes called LSX) are time-consuming or require unusual reaction conditions (such as high pressure) and are therefore impractical. Probably for these reasons, there has been no commercial use of LSX zeolite in detergents and little research into the use of similar zeolites such as Maximum Aluminum X-type zeolite, at least insofar as can be ascertained from the technical literature.
The known prior art comprises the following:
U.S. Pat. No. 4,094,778 teaches the combination of zeolite A and zeolite X as a detergent builder. In such a combination, the X-type zeolite is employed to scavenge the large hardness ions such as hydrated magnesium and iron while A-type zeolite efficiently removes calcium. A drawback of such an approach inheres in the low ion exchange capacity of standard (i.e., not Maximum Aluminum) X-type zeolites which necessitates increased total zeolite percentages in the detergent mixture.
British Pat. No. 1,580,928--Kuhl and Sherry--discloses the preparation of a large pore faujasite, (see definitions) referred to as "Low silica faujasite-type zeolite." This zeolite has a high ion exchange capacity (equal to A-type zeolites) and large pore size which enables it to exchange all significant hardness ions, including hydrated magnesium and iron ions. While the zeolite taught by British Pat. No. 1,580,928 would seemingly function well as a detergent builder, synthetic routes taught therein to produce the low-silica faujasite, appear to be commercially impractical.
According to the Kuhl and Sherry British Patent, low silica faujasite-type zeolite is produced by aging alumino silicate gels at temperatures generally below 45.degree. C. for two to three days in a highly alkaline mixed Na.sup.+ /K.sup.+ system. The aged mixture is subsequently crystallized at 60.degree. to 100.degree. C. The long precrystallative aging period is said to be important in the formulation of low-silica faujasite. Otherwise, it is indicated that immediate crystallization leads to the formation of high alumina content zeolite A. The general process description of Kuhl and Sherry suggests also the possibility of a single stage reaction to produce a predominantly low-silica faujasite product by holding the reaction mixture for several days at a temperature of below 50.degree. C.
East German Pat. Nos. 43,221 and 58,957, to Wolf, both teach the synthesis of X-type zeolites from alumino silicate gels at 50.degree.-100.degree. C. in 7 to 10 hours, but there is little indication in these patents that the zeolite product is of the Maximum Aluminum variety. As in the Kuhl and Sherry British patent, the starting materials demonstrated by the East German patents to Wolf do not include clays or other inexpensive alumino silicate sources, but rather are synthetic aluminosilicate gels. According to Wolf, this may include sodium aluminate or aluminum oxide, sodium waterglass or silica sol, sodium hydroxide, potassium hydroxide and water. Wolf's product is indicated to be a "sodium/potassium X zeolite." Further, at the temperature given in the example of East German Pat. No. 43,221 (70.degree.-75.degree. C.), experimental work by the present inventors indicates an extremely high percentage yield of predominantly A-type zeolite, if clay derived reactants are employed. Attempts by the Applicants herein to directly convert meta kaolin at 60.degree. , 70.degree. and 80.degree. C. under conditions comparable to those specified in the Wolf '221 patent have failed to produce high concentrations of Maximum Aluminum X-type zeolite in a variety of reaction mixtures.
U.S. Pat. Nos. 4,289,740 and 4,407,782 to Estes teach the synthesis of a high aluminum content zeolite HP from an aqueous solution of Na.sub.2 O, Al.sub.2 O.sub.3, and SiO.sub.2 at pressures of about 20,000 psig (138 MPa). Such zeolite HP is described by Estes as having ion exchange, catalytic, and absorptive properties which differ from known prior art X-type zeolites.
U.S. Pat. No. 3,114,603 to Howell teaches the synthesis of A-type zeolite from "reactive Kaolin-type clay material" by a two-step process similar to the digestion/crystallization taught by Kuhl and Sherry.